In order to quantify losses of nanometer-sized particle.; in turbulent flows through tubes, their penetration efficiencies were measured as a function of the particle size, Stokes number and Reynolds number. The penetration efficiency of tungsten oxide and ammonium nitrate particles with diameters between 3 a rid 17 nm was investigated in turbulent flow conditions with Reynolds numbers (Re) extending from 4500 to 10,500. The measured penetration efficiencies in straight tubes were found to deviate from the empirical correlation of Lee and Gieseke (1994). In contrast, the empirical equation of Fan and Ahmadi (1993) agrees better with our experimental results, also in comparison with the corresponding Wells and Chamberlain (1967) and Wood (1981) empirical correlation. Additional experiments were conducted to quantify the penetration efficiency of nanoparticles in tubes having 90 degrees bends for Dean numbers between 1426 and 2885. Penetration efficiencies of particles through 90 degrees bends were found to increase with increasing curvature ratios. The influence of Reynolds number (when varied between 4500 and 10,500) on the penetration efficiencies was found to be insignificant within the uncertainty of the measurements. We compared our experimental results of the penetration efficiencies through 90 degrees bends as a function of the Stokes number with the Pui et al. (1987) parameterization which was validated for particles larger than 100 nm. For particles larger than 12 nm our data agree with the Pui et al. (1987) parameterization. However, for smaller particles the measured penetration efficiencies increased with the Stokes number while their parameterization predicts the opposite. (C) 2012 Elsevier Ltd. All rights reserved.